Exterior and interior wall structures commonly are coated with a surface coating such as paint, sealer, textured coatings, stucco and so on. These surface coatings have various characteristics, including color, texture, moisture permeability and vapor permeability. It is desirable to have a surface coating that acts as a moisture barrier, but also allows the coated surface to breathe. This is because if the coating acts as a vapor barrier, this can lead to moisture build up, spotting, chipping, cracking, peeling, of the surface coating. Likewise, mildew can build up in the coated surface, and biological growth can occur, such as the growth of algae.
Resistance to moisture penetration, combined with vapor or gas permeability, is commonly viewed to be favorable characteristics of surface coatings. Accordingly there is a need to demonstrate or test these characteristics. For example, there is a need to demonstrate these characteristics to purchasers, users or consumers of surface coatings.
One apparatus for measuring vapor transmission rates is used in testing laboratories. Such an apparatus may use a cup or other enclosure with a permeable surface across an opening. The surface may be coated with the substance to be tested. Likewise a desiccant is placed inside the cup to absorb vapor. The cup is then placed in an environment with a known humidity level. As the desiccant in the interior of the cup absorbs moisture transmitted through the coated barrier, the cup can be weighed to determine the weight increase and therefore the vapor transmission rate.
This known apparatus suffers from various deficiencies for use as a demonstration or testing device. For example, it takes a relatively long period of time for moisture to transfer through the vapor barrier. Likewise, a measuring apparatus is required in order to determine the increase in weight of the cup as the desiccant absorbs moisture. Moreover, the transmission of the vapor or gas cannot easily be seen visually, or the liquid permeability is not readily observed. Without such visual demonstrability, the use of the known apparatus as a demonstration tool is somewhat limited.
Accordingly, there is a need for a demonstration and testing apparatus illustrating permeability characteristics of a surface coating.